1. Field of the Invention
The invention concerns a fixed glazing for improved acoustic protection for vehicles, specifically for automobiles, which is in contact with a peripheral seal. According to the invention, the glazing lacks one or more modes of radiation which are coupled with one or more acoustic cavity modes of the vehicular interior when the glass is excited by an acoustic field.
2. Discussion of the Background
Among the comfort qualities in modem transportation, such as in trains and automobiles, silence is crucial. Indeed, the other sources of discomfort--mechanical, of thermal origin, visibility problems, etc, --have been more or less taken care of. However, improving acoustic comfort presents new problems. It has been partly possible to deal with noises stemming from aerodynamics at their source, that is, noise created by air turbulence. This means that for economizing on energy, the shapes have been modified. Air penetration has been improved, and the turbulence which is itself a source of noise has been diminished.
Among the walls of a vehicle that separate the source of exterior aerodynamic noise from the interior space where the passenger sits, the glass is much more difficult to deal with. One cannot use the pasty or fibrous noise absorbing materials in glass like the ones used in opaque walls, and for reasons of weight, the glass thickness cannot be excessively increased. European patent EP-B1-0387 148 proposes glass which provides good insulation against noise of aerodynamic origin without increasing weight and/or thickness too much. This patent proposes a laminated glazing, the insert of which possesses good sound deadening properties.
Other noises such as motor noises, rolling noises or suspension noises must also be dealt with. These noises have already been dealt with at their origin or, in part, during their propagation, either through the air ( by absorbent sheeting in particular) or through solids (elastomer connecting elements, for example). In contrast, the design of glass so as to absorb noise which has its origin in the vehicle itself, that is, noise transmitted by way of the air or by the intermediary of solids, is more difficult to realize and is yet to be mastered.
The glazing constitutes an important surface of the interior of the vehicle and, consequently, an important surface of propagation. It turns out that using adapted connecting pieces is insufficient for avoiding the propagation of noise due to vibration of the glass, and that at certain speeds of rotation of the motor, a humming occurs that is perceptible by the passenger and thus becomes a source of discomfort. In fact, the rotation of the motor creates vibrations which are transmitted to the glass panes through the air or through solids.
The main parameters influencing the vibro-acoustic behavior of glass panes in this respect reside in the shape of the glass, the structure of the glass, the glass/interior interface, the exciting source and the mode of propagation. Thus, for a given vehicle, the ways of improving the behavior of the panels which the glass panes constitute include the structure of the glass as well as in the glass/vehicle interface.
Numerous efforts have been undertaken in modifying the structure of the glass in order to improve the sound muffling effect in the vehicle interior. In general, one can modify the construction of laminated glass panes, the insert of which possesses properties conferring protection against aerodynamic sound and/or noises of aerial origin and/or noise of solid origin, as well as the creation of multiple, panes of glass. In contrast, the use of such glass in the assembly of a vehicle considerably increases the cost of the vehicle.